The availability and low cost of ammonium nitrate (AN) have resulted in its widespread use in explosive formulations for commercial blasting. The simplest of these formulations is a mixture of AN and fuel oil (ANFO) in the ratio of approximately 94.5:5.5 by weight. Other formulations include a wide assortment of slurries and emulsions which have been developed to provide advantages over ANFO in handling, water resistance and improved performance.
The success of commercial AN formulations has attracted attention to the possible use of AN as a major ingredient in military explosives. For military applications, however, the developmental thrust has been directed primarily at ways of utilizing more effectively the energy available from explosives containing AN. Typically, AN formulations do not behave ideally in the explosive sense in that the energy release is not sufficiently prompt to yield theoretically possible detonation velocities and pressures. Development of methods to correct this deficiency has been an important part of military oriented research and development efforts over the past several years.
One approach has been to form low-melting eutectics comprised of AN and one or more explosive fuels. Eutectics offer increased intimacy of the ingredients, low melting points near those normally used in loading plants, and melt-cast properties compatible with conventional loading operations. Increased intimacy of the ingredients results in improved performance in some instances.
Typical of the eutectic composite formulations is one comprised of ethylenediamine dinitrate (EDD) and AN in the ratio 49:51 by weight (EA) with a melting point of approximately 103.degree. C. When the AN portion is modified to contain a ratio of 85:15 AN/KNO.sub.3 by weight, the formulation is called EAK. Potassium nitrate (KNO.sub.3) has been added to phase stabilize the AN. Other modifications may include an additional ingredient, such as nitroguanidine, which lowers the melting temperature still further, to approximately 98.degree. C., when present to the extent of 8% by weight of the composition (NEAK). Another formulation typical of an AN based composite explosive is a 2:1 mole ratio of AN:ammonium 3,5-dinitro-1,2,4-triazolate.
A co-pending patent application, entitled Eutectic Microknit Composite Explosives (EMCX), teaches methodology by which essentially anhydrous emulsions of composite formulations such as EAK may be handled as a supercooled fluid while being loaded into containers before setting to a hard consistency.
Two U.S. Pat. Nos. 4,248,644 and 4,391,659, also teach emulsification technology in similar formulations. This prior art differs in part from EMCX technology in that the products retain a grease-like consistency, or are at least extrudeable and do not solidify. The first of the above cited patents limits the fuel concentration to a minimum of 2.5% and the emulsifier to a minimum of 1% by weight for a total of 3.5% by weight. The second patent deals with water-in-fuel emulsions as the final products.
It has not been apparent heretofore that grease-like, oil-continuous emulsified compositions can be made with significantly reduced oil phase and emulsifier concentrations. In fact, some emulsions have been found, as shown in the invention described below, to increase in stability, and to retain grease-like characteristics when the oil phase concentrations have been reduced substantially below those practiced in the prior art.